Peening, as understood in the art and as used herein, means to compress a portion of a surface by forming a depression or indentation on the surface. Peening equipment generally is utilized to create a compressively stressed protection layer at the outer surface of a workpiece. The protection layer considerably increases the resistance of the workpiece to fatigue failure.
One known type of peening is referred to as shot peening. Shot used in shot peening generally are spherical particles constructed from a hard metal. With shot peening systems, a stream of shot traveling at a high velocity is directed at an outer surface of a workpiece. Each shot particle that impacts with sufficient force upon the outer surface of the workpiece causes plastic deformation of the surface and a dimple is formed therein. In this manner, a compressively stressed layer is formed at the outer surface of the workpiece.
In order to accurately control a shot peening process and the results thereof, several variables must be accurately controlled. These variables include the size, shape and velocity of each shot particle. Systems and methods are available to control these variables, however, these systems increase the cost of the peening process. Moreover, it is very difficult to precisely and continuously control shot size, shape and velocity, and in practice, a percentage of deviation from predetermined values is tolerated. This leads to uncertainty as to the actual results of a shot peening process and earlier-than-predicted failure of the workpiece may occur. This is very undesirable because a replacement for the workpiece may not be readily available and causes loss of time and resources.
In operation, shot peening systems usually are very noisy and require an enclosed area with noise suppression. These systems also require ventilation systems for removal of dust particles. Noise suppression and ventilation systems further increase the cost of peening systems. Also, while peening a workpiece, it often is desirable to accurately peen only a specific area of the workpiece surface. With slot peening systems, however, stray shot sometimes undesirably peen a surface outside the specific area. In some instances, this stray peening may require that the entire workpiece be discarded.